This invention relates to new photoresist materials which can be used to directly achieve a positive image of a desired pattern on a substrate and to methods for their us which eliminate the conventional developing step.
Printed circuit boards, ubiquitous components of modern electronic equipment, are manufactured by the millions using photoresists. Typically, the photoresist is a thin layer of a photoreactive monomer which polymerizes on exposure to light, changing from a soluble to an insoluble form. Like a photographic plate, the image is a negative one developed by solvent removal of the unexposed areas. This development step contributes a significant amount to the overall cost of printed circuit production. Its elimination could, therefore, reduce costs by a considerable amount.
Heretofore, the polysilane class of polymers has not been applied in photoresist technology. However, polysilanes are known. For example, West et al, J.A.C.S. 103, 7352 (1981) discloses (phenylmethylcodimethyl) silane as a solid film which crosslinks under UV irradiation. Ishikawa et al, J. Organometallic Chem., 42, 333 (1972) discloses the preparation of permethylpolysilanes which degrade to non-volatile octamethyltrisilane and other polymeric materials upon exposure to UV irradiation in solution. Wesson et al, J. Poly. Sci., Polym. Chem. Ed., 7, 2833 (1979) discloses the preparation of polydimethylsilane. Wesson et al, op. cit., 19, 65 (1981) discloses block copolymers of ethylmethyl- and dimethyl-silane units. Wesson et al, op. cit., 18, 959 (1980) discloses the preparation of copolymers of ethylmethylsilane units with dimethylsilane units as well as of methyl/propyl units with dimethyl units. In addition, U.S. Pat. Nos. 2,544,976, 4,052,430, 2,612,511 and 4,276,424 disclose preparation of other silane-type photoresists.
There remains a need to provide photoresists which are simpler and easier to use and which have the properties desirable in the photopatterning process used, e.g., in the microelectronics industry. At the same time, it is desirable to extend the range of uses of the polysilanes into this area.